Commands of this namespace enable user to define a BWidget or a
Tk widget as a drop site. A drop site is composed of the type of
object that can be dropped and associated operation, a command
called when drop occurs, and a command when an object is dragged
over the widget. A drop site must have at least one type of
acceptable object and a drop command.

This command provides a simple way to include options relatives
to a drop site into BWidget resources definition. It includes the
options needed for register, -dropovercmd and
-dropcmd, initialized to empty string, and
-droptypes, initialized to types, and one new option:

This command can be used to provide a dynamic drag while
drag-over events. While a drag occurs, events <Enter>,
<Motion> and <Leave> are catched. Arguments passed to
the command are:

pathname of the drop target (the widget itself),

pathname of the drag source,

event over the drop target: enter, motion or
leave,

root x-coordinate of the pointer,

root y-coordinate of the pointer,

operation,

type of the dragged data,

dragged data.

Command must the new status of the drag:

0 if widget refuse this drag. Command will not be recalled on
motion/leave event.

1 if widget accept this drag. Command will not be recalled on
motion/leave event.

2 if widget refuse this drag. Command will be recalled on each
motion event to reevaluate.

3 if widget accept this drag. Command will be recalled on each
motion event to reevaluate.

Here is a list of events and associated actions on a DropSite
widget. This example assumes that dragged data type is valid for
the drop target. status is the status of the drag on a
DropSite. Its value is:

Specifies a list {typeoplist ?typeoplist? ...} of acceptable types and associated operations
for the drop target. For each type, oplist is a list
{descopsmod ?descopsmod? ...}
describing operations and modifier keys for these operations.
descops describe an operation. It can be a predefined
operations (copy, move or link) or a new user
defined operation, of the form {subopbaseop
?bitmap?}. subop is the name given to the sub
operation, baseop is the name of the base operation
(copy, move or link) and bitmap is a
bitmap to display for the operation.
If bitmap is empty, the default bitmap of the base operation
is used for the sub operation.subop can be a base operation, in order to change the bitmap
of a base operation. In this case, baseop must be empty or
equal to subop.mod is the modifer key for the operation. It can be:

none to specify that no modifier key is pressed. This
modifier can only be used with a sub operation named default
(and vice versa), which has the behaviour of not display any bitmap
operation. For all type, if the modifier none is not given,
it is automatically associated to the default sub operation
of a copy base operation.

program to specifies a sub operation accessible only by
DropSite::setoperation.

A list combining shift, control and alt,
which means their corresponding key.

This command provides a simple way to call register
during a BWidget creation or configuration.

path is the pathname of the BWidget,

subpath is the pathname of the tk widget where drag
event occurs,

dropover is a command for drag-over event,

drop is a command for drop event,

force specifies wether or not to call register
whenever no option value has changed (0 by default - for BWidget
configuration, use 1 for BWidget creation).

setdrop verifies the modification flag of options
dropenabled and droptypes and calls register
if needed according to the options values and dropover and
drop arguments. dropovercmd and dropcmd are
not taken from options of widget because they are considered as
user command, called by BWidget implementation of drag-over
and drop events.